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Introduces rtc_base/synchronization/mutex.h.

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This change introduces a new non-reentrant mutex to WebRTC. It
enables eventual migration to Abseil's mutex.

The mutex types supportable by webrtc::Mutex are

- absl::Mutex
- CriticalSection (Windows only)
- pthread_mutex (POSIX only)

In addition to introducing the mutexes, the CL also changes
PacketBuffer to use the new mutex instead of rtc::CriticalSection.

The method of yielding from critical_section.cc was given a
mini-cleanup and YieldCurrentThread() was added to
rtc_base/synchronization/yield.h/cc.

Additionally, google_benchmark benchmarks for the mutexes were added
(test courtesy of danilchap@), and some results from a pthread/Abseil
shootout were added showing Abseil has the advantage in higher
contention.

Bug: webrtc:11567, webrtc:11634
Change-Id: Iaec324ccb32ec3851bf6db3fd290f5ea5dee4c81
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/176230
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Tommi <tommi@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31443}
This commit is contained in:
Markus Handell
2020-06-04 00:41:20 +02:00
committed by Commit Bot
parent e917379c5b
commit f70fbc8411
24 changed files with 779 additions and 44 deletions
Download Patch File Download Diff File Expand all files Collapse all files

1
modules/video_coding/BUILD.gn
View File

@ -192,6 +192,7 @@ rtc_library("video_coding") {
"../../rtc_base/experiments:min_video_bitrate_experiment",
"../../rtc_base/experiments:rate_control_settings",
"../../rtc_base/experiments:rtt_mult_experiment",
"../../rtc_base/synchronization:mutex",
"../../rtc_base/synchronization:sequence_checker",
"../../rtc_base/task_utils:repeating_task",
"../../rtc_base/third_party/base64",

12
modules/video_coding/packet_buffer.cc
View File

@ -78,7 +78,7 @@ PacketBuffer::~PacketBuffer() {
PacketBuffer::InsertResult PacketBuffer::InsertPacket(
std::unique_ptr<PacketBuffer::Packet> packet) {
PacketBuffer::InsertResult result;
rtc::CritScope lock(&crit_);
MutexLock lock(&mutex_);
uint16_t seq_num = packet->seq_num;
size_t index = seq_num % buffer_.size();
@ -136,7 +136,7 @@ PacketBuffer::InsertResult PacketBuffer::InsertPacket(
}
void PacketBuffer::ClearTo(uint16_t seq_num) {
rtc::CritScope lock(&crit_);
MutexLock lock(&mutex_);
// We have already cleared past this sequence number, no need to do anything.
if (is_cleared_to_first_seq_num_ &&
AheadOf<uint16_t>(first_seq_num_, seq_num)) {
@ -173,25 +173,25 @@ void PacketBuffer::ClearTo(uint16_t seq_num) {
}
void PacketBuffer::Clear() {
rtc::CritScope lock(&crit_);
MutexLock lock(&mutex_);
ClearInternal();
}
PacketBuffer::InsertResult PacketBuffer::InsertPadding(uint16_t seq_num) {
PacketBuffer::InsertResult result;
rtc::CritScope lock(&crit_);
MutexLock lock(&mutex_);
UpdateMissingPackets(seq_num);
result.packets = FindFrames(static_cast<uint16_t>(seq_num + 1));
return result;
}
absl::optional<int64_t> PacketBuffer::LastReceivedPacketMs() const {
rtc::CritScope lock(&crit_);
MutexLock lock(&mutex_);
return last_received_packet_ms_;
}
absl::optional<int64_t> PacketBuffer::LastReceivedKeyframePacketMs() const {
rtc::CritScope lock(&crit_);
MutexLock lock(&mutex_);
return last_received_keyframe_packet_ms_;
}

46
modules/video_coding/packet_buffer.h
View File

@ -22,8 +22,8 @@
#include "modules/rtp_rtcp/source/rtp_packet_received.h"
#include "modules/rtp_rtcp/source/rtp_video_header.h"
#include "rtc_base/copy_on_write_buffer.h"
#include "rtc_base/critical_section.h"
#include "rtc_base/numerics/sequence_number_util.h"
#include "rtc_base/synchronization/mutex.h"
#include "rtc_base/thread_annotations.h"
#include "system_wrappers/include/clock.h"
@ -83,67 +83,67 @@ class PacketBuffer {
~PacketBuffer();
InsertResult InsertPacket(std::unique_ptr<Packet> packet) ABSL_MUST_USE_RESULT
RTC_LOCKS_EXCLUDED(crit_);
RTC_LOCKS_EXCLUDED(mutex_);
InsertResult InsertPadding(uint16_t seq_num) ABSL_MUST_USE_RESULT
RTC_LOCKS_EXCLUDED(crit_);
void ClearTo(uint16_t seq_num) RTC_LOCKS_EXCLUDED(crit_);
void Clear() RTC_LOCKS_EXCLUDED(crit_);
RTC_LOCKS_EXCLUDED(mutex_);
void ClearTo(uint16_t seq_num) RTC_LOCKS_EXCLUDED(mutex_);
void Clear() RTC_LOCKS_EXCLUDED(mutex_);
// Timestamp (not RTP timestamp) of the last received packet/keyframe packet.
absl::optional<int64_t> LastReceivedPacketMs() const
RTC_LOCKS_EXCLUDED(crit_);
RTC_LOCKS_EXCLUDED(mutex_);
absl::optional<int64_t> LastReceivedKeyframePacketMs() const
RTC_LOCKS_EXCLUDED(crit_);
RTC_LOCKS_EXCLUDED(mutex_);
private:
Clock* const clock_;
// Clears with |crit_| taken.
void ClearInternal() RTC_EXCLUSIVE_LOCKS_REQUIRED(crit_);
// Clears with |mutex_| taken.
void ClearInternal() RTC_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
// Tries to expand the buffer.
bool ExpandBufferSize() RTC_EXCLUSIVE_LOCKS_REQUIRED(crit_);
bool ExpandBufferSize() RTC_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
// Test if all previous packets has arrived for the given sequence number.
bool PotentialNewFrame(uint16_t seq_num) const
RTC_EXCLUSIVE_LOCKS_REQUIRED(crit_);
RTC_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
// Test if all packets of a frame has arrived, and if so, returns packets to
// create frames.
std::vector<std::unique_ptr<Packet>> FindFrames(uint16_t seq_num)
RTC_EXCLUSIVE_LOCKS_REQUIRED(crit_);
RTC_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
void UpdateMissingPackets(uint16_t seq_num)
RTC_EXCLUSIVE_LOCKS_REQUIRED(crit_);
RTC_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
rtc::CriticalSection crit_;
mutable Mutex mutex_;
// buffer_.size() and max_size_ must always be a power of two.
const size_t max_size_;
// The fist sequence number currently in the buffer.
uint16_t first_seq_num_ RTC_GUARDED_BY(crit_);
uint16_t first_seq_num_ RTC_GUARDED_BY(mutex_);
// If the packet buffer has received its first packet.
bool first_packet_received_ RTC_GUARDED_BY(crit_);
bool first_packet_received_ RTC_GUARDED_BY(mutex_);
// If the buffer is cleared to |first_seq_num_|.
bool is_cleared_to_first_seq_num_ RTC_GUARDED_BY(crit_);
bool is_cleared_to_first_seq_num_ RTC_GUARDED_BY(mutex_);
// Buffer that holds the the inserted packets and information needed to
// determine continuity between them.
std::vector<std::unique_ptr<Packet>> buffer_ RTC_GUARDED_BY(crit_);
std::vector<std::unique_ptr<Packet>> buffer_ RTC_GUARDED_BY(mutex_);
// Timestamp of the last received packet/keyframe packet.
absl::optional<int64_t> last_received_packet_ms_ RTC_GUARDED_BY(crit_);
absl::optional<int64_t> last_received_packet_ms_ RTC_GUARDED_BY(mutex_);
absl::optional<int64_t> last_received_keyframe_packet_ms_
RTC_GUARDED_BY(crit_);
RTC_GUARDED_BY(mutex_);
absl::optional<uint32_t> last_received_keyframe_rtp_timestamp_
RTC_GUARDED_BY(crit_);
RTC_GUARDED_BY(mutex_);
absl::optional<uint16_t> newest_inserted_seq_num_ RTC_GUARDED_BY(crit_);
absl::optional<uint16_t> newest_inserted_seq_num_ RTC_GUARDED_BY(mutex_);
std::set<uint16_t, DescendingSeqNumComp<uint16_t>> missing_packets_
RTC_GUARDED_BY(crit_);
RTC_GUARDED_BY(mutex_);
// Indicates if we should require SPS, PPS, and IDR for a particular
// RTP timestamp to treat the corresponding frame as a keyframe.